This invention relates to the manufacture of solid metal spherical articles. The invention is particularly applicable to the manufacture of lead shot for shotgun cartridges, more particularly the larger or heavier gauge shot, but is also suitable for other products such as spherical lead weights for fishing tackle, for example.
Small gauge lead shot is produced by allowing droplets of liquid lead to fall under gravity down a so-called shot tower into water. However, for larger sizes of shot, for example 0.2 inch diameter, the shot tower process is not practicable because the surface tension of the shot material breaks down. For the larger sizes of shot, methods employed have involved mechanically forming each part in a mould.
In order to provide spherical lead shot, experiments have been carried out to tumble in a barrel a quantity of lead preforms in the shape of short lengths severed from a wire. The experiments were generally satisfactory for small quantities of shot although a long cycle time, in excess of ten hours, was required. This was uneconomic for commercial requirements.